1. Field of the Invention
This invention pertains to exercise machine, and more particularly to apparatus that produces different loads during concentric and eccentric muscle functions of an exercising person.
2. Description of the Prior Art
The physiology of human muscles enables them to function in three different ways. The first is a positive or concentric function in which the muscles contract under a load that is less than the muscle strength. The second way is a static or isometric function in which the muscle attempts to contract against a load that is greater than the muscle strength. The third muscle function is a negative or eccentric function in which an external load is large enough to overcome the muscle strength and force the muscle to elongate in spite of an attempt by the person to contract the muscle.
It is well known that muscles perform much more efficiently during eccentric functions than during concentric or isometric functions. The same muscle can exert a greater force during eccentric functions than it can during either concentric or isometric functions. In addition, the energy expended, and the associated electrical activities or pulses of the muscle nervous system, are greater during concentric and isometric functions compared to eccentric functions when overcoming the same load.
Various types of equipment have been developed to assist persons exercise their muscles. The equipment ranges from simple hand-held barbells to complicated and expensive hydraulically controlled machines. Many machines are very specialized in that they are designed to exercise only one or a very limited set of muscles.
With only very few exceptions, prior exercise machines have not taken advantage of the muscle physiology related to the differences in efficiency between concentric and eccentric functions. Almost all known prior machines impose a single load that the person must overcome during both concentric and eccentric muscle functions. A few prior exercise machines were capable of imposing different loads for concentric and eccentric muscle functions, but those machines invariably included very expensive and complicated hydraulic systems.
Examples of prior mechanical exercise machines are plentiful. The Powertec Direct Company of Milford, Pa., markets a wide variety of equipment for exercising many of the body's muscles such as legs, back, chest, thigh, and arms. The Hammer Strength Company of Cincinnati, Ohio, and Promaxima Manufacturing Limited of Houston, Tex., also market respective lines of mechanical exercising equipment.
Many of the commercially available exercise machines utilize one or more pivoting beams. One end of the beam is pivoted to a frame. The beam supports one or more weights. The exercising person oscillates the beam and weights by alternately performing concentric and eccentric functions by the appropriate muscles. The beam and weight design of prior equipment imposes the same load for both the concentric and eccentric muscle functions.
A typical example of prior equipment is the bench press, such as is marketed by the Powertec Direct Company. Somewhat similar equipment is shown in PCT patent WO89/01805. Other examples of beam and weight type exercising machines may be seen in U.S. Pat. Nos. 5,050,873; 5,066,003; 5,125,881; 5,135,449; 5,135,456; 5,171,198; 5,180,354; 5,181,896; 5,273,504; 5,273,505; and Des 321,391. No machine of the foregoing patents gives any indication that different loads should be overcome by the person during concentric and eccentric functions of his muscles.
U.S. Pat. No. 4,826,155 shows equipment that takes into account the inherent ability of human muscles to perform differently during concentric and eccentric functions. The U.S. Pat. No. 4,826,155 shows a harness that is worn by an exercising person. A spotter operates a rope that is tied to the harness through a block and tackle in order to assist the person to raise weights during concentric muscle functions. During the eccentric muscle functions, the spotter allows an increased load to be imposed on the exercising person.
Despite the widespread availability of numerous different kinds of exercise machines, further improvements to them are desirable.